Device for transmitting accurate translational and rotary movements

ABSTRACT

A device for transmitting accurate translational and rotary movements includes a rotary input shaft on which is mounted a rotary driving cam which is engaged with a pivotal follower carried on a lever which is pivotally mounted at its one end and has said follower intermediate its length so that the lever is moved backwardly and forwardly. The lever carries a drive roller at its outer end which engages in an annular slot of a disc carried on an output shaft and oscillation of the lever by movement of the cam causes a back and forward axial displacement of the output shaft. Rotary movement is imparted to the output shaft after it first moves through a path in which it is constrained against rotary movement by two roller members which are carried on a fixation piece affixed to the shaft and which are guided on respective sides of an elongated keyway of the housing. The rollers move out of engagement with the keyway after a pinion gear carried on the shaft is moved into meshing engagement with a rack which is carried on a slide which is mounted for movement backwardly and forwardly on one or more guide rods. The slide also carries a follower which is moved by a different cam part and, when it is in meshing engagement with the pinion gear, it produces a controlled rotation of the output shaft. A ribbed barrel cam is employed for effecting accurate rotational movement of the output shaft through the use of two roller followers arranged on respective sides of the ribbed cam and which are preloaded against the cam. The rack is arranged so that it is at a slight angle in respect to the horizontal so that it provides an easy entry of the sliding rotatable pinion gear and meshes therewith without interference after engagement.

States Patent [191 Beezer DEVICE FOR TRANSMITTING ACCURATE TRANSLATIONALAND ROTARY MOVEMENTS [75] Inventor: Earl F. Beezer, Hillsdale, NJ.

[73] Assignee: Stelron Cam Company, Saddle Brook, NJ.

[22] Filed: Feb. 11, 1974 [2]] Appl. No.: 441,489

Primary Examiner-Wesley S. Ratliff, Jr.

[57] ABSTRACT A device for transmitting accurate translational androtary movements includes a rotary input shaft on which is mounted arotary driving cam which is engaged with a pivotal follower carried on alever which is pivotally mounted at its one end and has said followerintermediate its length so that the lever is [451 Mar. 11, 1975 .movedbackwardly and forwardly. The lever carries a drive roller at its outerend which engages in an annular slot of a disc carried on an outputshaft and oscillation of the lever by movement of the cam causes a backand forward axial displacement of the output shaft. Rotary movement isimparted to the output shaft after itfirst moves through a path in whichit is constrained against rotary movement by two roller members whichare carried on a fixation piece affixed to the shaft and which areguided on respective sides of an elongated keyway of the housing. Therollers move out of engagement with the keyway after a pinion gear.carried on the shaft is moved into meshing engagement with a rack whichis carried on a slide which is mounted for movement backwardly andforwardly on one or more guide rods. The slide also carries a followerwhich is moved by a different cam part and, when it is in meshingengagement with the pinion gear, it produces a controlled rotation ofthe output shaft. A ribbed barrel cam is employed for effecting accuraterotational movement of the output shaft through the use of two rollerfollowers arranged on respective sides of'the ribbed cam and which arepreloaded against the cam. The rack is arranged so that it is at aslight angle in respect to the horizontal so that it provides an easyentry of the sliding rotatable pinion gear and meshes therewith withoutinterference after engagement.

12 Claims, 8 Drawing Figures PATENTED MAR I I I975 8M1 2 UF 4 FIG.2

F'IG.5

DEVICE FOR TRANSMITTING ACCURATE TRANSLATIONAL AND ROTARY MOVEMENTSBACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates in general to the construction of automatic motion transmittingmachines and, in particular, to a new and useful device for transmittingaccurate translational and rotary movements to an output shaft from arotary input shaft.

2. Reference to Prior Issued Patent The present invention is animprovement over the invention disclosed and claimed in US. Pat. No.3,731,545 by the present inventor in respect to the means forcontrolling the rotational movement of the output shaft and in respectto the construction which permits a wider selection of the start andstopping of the rotational movement.

DESCRIPTION OF THE PRIOR ART As indicated in US. Pat. No. 3,731,545, itis known to provide a mechanism for transmitting accurate translationaland rotary movements from a rotary input shaft to an output shaft. Withthe known device, the movement is transmitted from rotary cams on theinput shaft to effect a translatory movement of the output shaft or ashifting of the output shaft in an axial direction. The apparatusincludes means for guiding the shaft axially so as to prevent itsrotation until a driving pinion on the output shaft is moved intomeshing engagement with a quadrant gear. A device of this characteroperates satisfactorily to produce most rotational and translatorymovements, but in some instancesit is desirable that the rotary drive beeffected through means which will ensure an easier means for engagingand disengaging the drive gears and for providing engagement withoutteeth interference and through a drive system which operates with aminimum of friction and play. In addition, it is desirable that theoperation of the output shaft can be effected through a complete 360rotational range and that the starting and stopping position may becontrolled at will so that no mechanical disadvantages result bystarting a particular angle of position of the output shaft.

SUMMARY OF THE INVENTION The present invention provides an improveddevice for transmitting accurate translational and rotary movement to anoutput shaft from a rotary input shaft, which includes a slide which ismovable backwardly and forwardly and which carries a rack gear whichengages with a pinion on the output shaft after the output shaft isfirst guided for linear axial movement by roller elements which bearagainst respective opposite sides of an elongated key. The rack slideadvantageously includes a roller follower which is preloaded against aribbed cam of a barrel cam so that it moves precisely and without play.The rack itself is cocked at a very slight angle to allow entry of thepinion gear which moves with the cam in an axial direction and whichrotates after engagement with the rack. This allows the entry of thesliding rotating gear at appropriate times without teeth interferenceand effects a slight pitch line interference when the rack and gear arein engagement in order to eliminate gear and rack backlash. The slidecarrying the rack moves backwardly and forwardly on linear ball bearingsin order to minimize friction. All

play is eliminated between the various parts which control the rotationof the output shaft and this is very important in actual operation sinceaccurate rotary positioning is of paramount importance.

The invention is kinematically an improvement over the prior art becauseof the construction which permits easy interengagement of the rotarypinion on the rotatable output shaft with the driving rack and thebeginning and end of rotation are constrained with no mechanicaldisadvantage. The start and stop position may be at any angular positionso that the control of the starting and stopping is not difficult.

In accordance with a further feature of the invention, the holding platecarrying constraining rollers which engage with an elongated axiallyextending keyway to constrain the shaft against rotation when it is notmeshed with the rack, are such that the operation of rotation may becarried out through 360 of movement and the starting-and stopping of therotational movement may be effected at any designed angle. Theconstruction is such that there is no requirement that the shaft bereturned to its original starting position before its axial androtational movements are begun.

Accordingly, it is an object of the invention to provide an improveddevice for transmitting accurate translational and rotary movement whichincludes an output shaft which is rotatable and axially movable underthe control .of a rotatable cam and which includes a rack gear drivingthrough a pinion gear contained on the output shaft,

A further object of the invention is to provide a device fortransmitting accurate translational and rotary movement which includesan output shaft which is axially displaceable and which is held againstrotation by one of a plurality of angularly spaced pairs of positionrollers which bear on respective opposite sides along the edges of a keywhich is affixed to a housing for the shaft and which also includes apinion gear on the shaft which is moved into engagement with a rack on aslide after the output shaft moves a predetermined amount in an axialdirection, the rack having a pitch which is cocked at a very slightangle to allow easy entry of the pinion gear on the output shaft whichmoves into engagement therewith and without teeth interference and alsoprovides a slight pitch line interference to eliminate gear and rackbacklash when the two gears are engaged.

A further object of the invention is to provide an improved motiontransmitting device which includes a slide which is guided for back andforth movement on linear ball bearings and which includes rollerfollowers which may be preloaded against respective side edges of aribbed barrel cam in order to transmit precise movements without play orbacklash to a rotary output shaft.

A further object of the invention is to provide a motion transmittingdevice which is simple in design, rugged in construction and economicalto manufacture.

For an understanding of the principles of the invention, reference ismade to the following description of a typical embodiment thereof asillustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the Drawings:

FIG. 1 is a front top perspective view with a portion of the housingbroken away of-a motion transmitting device constructed in accordancewith the invention;

FIG. 2 is a section taken along the line 22 of FIG. 1;

FIG. 3 is a section taken alongthe line-3-3 of FIG.

FIG. 4 is a section taken alongthe line 4-4 of FIG.

FIG. 4ais a section taken along the line 4a4a of FIG. 4; 5

FIG. 5 is a timing-diagram for the operation of the de- FIG. 6 is atiming diagram for a back and forth oscillation of the output shaft; and

FIG. 7 isa timingdiagram for effecting continuous intermittent rotationand lift of the output shaft.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to the drawings inparticular, the invention embodied therein, comprises a motiontransmitting device including a housing, generallydesignated 10, of ablock-shaped configuration having a rounded end portion 10a and with afront wall 12 in which is rotatably mounted an input shaft 14. The inputshaft extends to the interior space 16 of the housing where it carriesearns 17 and 18. The cam 17 is a plate or disc cam, and it has aninterior face 17a with a cam groove 17b which is engaged by a rollerfollower 20 of'an oscillatable drive lever 22. Drive lever 22 is securedto a shaft 24 which is journalled in front wall 12 and rear wall 23close to a bottom wall 25. The upper end of lever 22 includes a drivemember 22a which engages in annular groove 26a of a control disc 26which is affixed to output shaft 28. The output shaft 28 is journalledin the recirculating linear ball bearing bushings 30 and 32 carried inrespective side walls 34 and 36. Ball bearing bushings 30 and 32 arecombination rolling and linear bearings and ensure an easy and accurateguidingof the shaft 28. When input shaft 14 is rotated, it causesrotation of cam 17 and oscillation of lever 22 through engagement of thefollower 20 in control groove or cam 17b, and this causes drive member22a to produce a back and forward axial sliding movement of output shaft28, in the directions indicated by the double arrow 38.

In accordance with a feature of the invention, output shaft 28 isimparted with a controlled rotational movement in addition to itscontrolled translatory movement, by a cam driving mechanism includingthe cam 18, which comprises a ribbed barrel cam having an outstandingribbed cam portion 180. Ribbed cam portion 18a imparts a controlledmovement to a slide, generally designated 40, which is guided on linearball bearings for front and back movement substantially parallel toinput shaft 14 on rods 43 and 44, which are supported in front wall 12and rear wall 23, respectively. Slide may be guided very accurately andwithout any loss of motion or inaccuracy because of the use of thelinear ball bearings and also because it includes drive rollers 40a and40b which engage against respective sides of the ribbed cam portion 18aand may be preloaded in engagement therewith so as to eliminate allbacklash and shake.

In accordance with a further feature of the invention, the slide 40carries a drive gear in the form of a rack 46 which meshes with a piniongear 48 carried on output shaft 28.

As shown in FIGS; 1 and 2, the pinion 48 is moved into engagement-withrack 46 when output shaft 28 is moved substantially to the end'of itslinear movement and this engagement is effected before output shaft 28is moved out of association with its linear guiding means, generallydesignated 50.

In accordance with a further feature of the invention, the rack 46 iscarried on slide 40 in a manner such that it makes a small angle 0 inrespect to gear 48, so that it is cocked at this very slight angle toallow easy entry of gear 48 when output shaft 28 is moved to effect thisinterengagement. The interengagement occurs without teeth interference,but when the gears are fully in mesh, they have a slight pitch lineinterference between them, in order to eliminate gear and rack backlash.Slide 40 carries linear ball bearings 52 and 54, which engage rods 43and 44, respectively-With the construction, all friction is minimized,and the play between the parts is eliminated so that the rotation ofoutput shaft 28 is controlled very accurately. This is a very importantconsideration when a device is employed for accurately placing variousmachine parts or operating parts independent on both the linear androtational movements of the output shaft 28.

In accordance with another feature of the invention, output shaft 28 isguided by shaft linear guiding means so that it moves axially withoutrotation except when the gear 48 is engaged with rack 46. Guiding means50 includes an axially elongated key 56 which is secured to the curvedportion of the housing 10a in a position to overlie shaft 28 on the sidethereof opposite to earns 17 and 18. Guiding means 50 includes a controlplate or disc, generally designated 58, which, as shown in FIG. 4, has arounded outer circumference 60 with a plurality of flats in this casefour 60a, 60b, 60c and 60d, which are provided for mounting pairs ofpositioning or holding rollers 62 and 64, which are mounted so that whenin operation, they bear against respective sides of the key 56. As shownin FIG. 4, the control plate 58 is provided with the plurality of flatswhich may be set by design in order to achieve a plurality of positionsin which the output shaft 28 to which it is affixedmay be .held when itis moved linearly. In the four positions shown in FIG. 4, the separatingangles between the various centers of the flats are indicated. In orderto provide for a further variation of the positioning of the shaft whenit is moved linearly, an additional key, such as a key 56a, may also beprovided, which, as indicated, is located 30 away from key 56.

The construction of a control plate 58 which permits the various outputshaft guidance arrangements provides an improved kinematic arrangementfor the mechanism for controlling both'the translatory and rotarymovement of output shaft 28. The arrangement ensures that there will beno mechanical disadvantage due to the requirement that the beginning orend of rotation of the shaft be effected at a predetermined angularposition thereof. Due to this arrangement, it is assured that there willbe no starting or stopping at a disadvantageous position in respect tothe operating cams l7 and 18 and there will be no limitations in respectto the angular position to an end 66a of an operational arm which isaffixed to the output shaft 28.

Thus, with the inventive arrangement, there is no requirement that thearm 66 be returned to a starting position before it is moved on its nextcycle. The mechanism is capable of operating in this manner, but it isalso possible with the arrangement, to complete a full 360 arc ofrotation and to effect a large variation of discrete angular incrementalmovements of shaft 28 and hence, the arm 66, as desired. An example ofsuch movements may be: two positions 180; four positions 90; fivepositions 72; six positions 60, and by adding a second lock key, such aslock key 5611 shown in FIG. 4, there may be additional positions up to8, 10, or 12, for example. The number of positions can be increased bymaking the component parts larger to accommodate more guide rollers 62and 64.

Rollers 62 and 64 may be pre'loaded against key 56, and for thispurpose, at least one roller, e.g. roller 64, is eccentrically mountedon a rotatable shaft 63 by a roller bearing collar 65. Shaft 63 isrotated to effect tight loading engagement of roller 64 on key 56 andthen it is locked in position such as by a clamp (not shown) engageablewith a flat on the shaft and thus all possibility of shake is eliminatedfrom the mechanism.

The arrangement of the invention also makes it possible for the unit tooperate as an oscillating device or function as an intermittentlyrotating device. In addition, the device may be used to effect rotationof the output shaft 28 to an angle of rotation such as 37 or 129 sincethe ribbed cam 18 produces a stroke movement which is a direct functionof the required gear pitch line distance corresponding to the requiredangle of oscillation.

The intermittent rotation of the device is accomplished by returning therack 46 to its starting position at a time when it is out of contactwith pinion gear 48 so that the next engagement can provide a continuousrotation in the same direction. It is necessary that an integral numberof teeth of the rack 46 and the pinion gear 48 go into and out ofengagement during each interengagement and to do this, the followingtable illustrates how this may be accomplished:

NO. NO. OF

OF TEETH ON NO. OF ANGLE OF TEETH ROTATE REVO- POSlTlONS ROTA INDEX GEARLU- TlON TlON 2 180 l 2 Teeth 24 Teeth /2 4 90 do. 48 do. /4) 6 72 8 do.40 do. (1/5) 6 60 8 do. 48 do. (1/6) 8* 45 6 do. 48 do. (Va) 10* 36 44do. 40 do. (mo) 12* 4 do. 48 d0. (1/12) Cam stroke /2 that of 4. 5, 6Positions.

In FIG. 5, a cam timing diagram is indicated for effecting intermittentrotation. It is possible to provide a standard unit which offers apredetermined linear movement of shaft 28 for a certain amount ofdegrees of timing of the cam and an oscillating movement with adifferent predetermined degree of timing if desired. The mechanism issuch that it is a simple matter to effect a changing of the timing whichmay be effected by rotation of the input shaft. For example, thestandard gearing may be with a 1:1 ratio for a certain amount of degreesof transfer of the oscillating arm 66 or with a 2:1 ratio for anotherpredetermined amount of degrees of movement.

Additionally, FIGS. 6 and 7 show timing diagrams for, respectively,effecting a back and forth oscillation movement of the output shaft anda progressive intermittent complete rotational movement and lift of theoutput shaft.

While a specific embodiment of the invention has been shown anddescribed in detail to illustrate the application ofthe principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles.

What is claimed is:

l. A motion transmitting device, comprising a rotary input shaft havingrotary control cam means thereon, a rotary and axially movable outputshaft having a pinion gear thereon, means supporting said input shaftfor rotary movement and said output shaft for rotary and axial movement,a lever engaged with said cam means and said output shaft and beingmovable by said cam means to shift said output shaft axially, rotarydrive means connected to said cam means and including a drive gear movedby said cam means engageable with said pinion gear to rotate said outputshaft when it is in a predetermined axial position, said pinion gearbeing disengageable from said drive gear to permit axial movementwithout rotation, and holder means to hold said output shaft againstrotation at positions of said output shaft when said pinion gear is outof engagement with said drive gear and to permit easy interengagement ofsaid gears including at least one key elongated in the axial directionof said shaft and fixed in said housing and a control plate affixed tosaid shaft for rotation therewith having a plurality ofcircumferentially spaced pairs of transversely spaced guide rollersadapted to bear along respective sides of said key to hold the saidoutput shaft in a fixed angular position during its linear movement.

2. A motion transmitting device, according to claim 1, wherein saidcontrol plate has a periphery with a plurality ofcircumferentiallyspaced flat chordal mounting surfaces for each of said sets of guiderollers.

3. A motion transmitting device, according to claim 1, wherein saiddrive gear comprises a rack, a slide carrying said rack, means in saidhousing for guiding said slide backwardly and forwardly.

4. A motion transmitting device, according to claim 3, wherein said cammeans includes a separate disc cam and ribbed barrel cam with anoutwardly projecting cam rib, said slide having a roller which ispreloaded against each side of said cam rib whereby said slide is movedwithout play backwardly and forwardly.

5. A motion transmitting device, according to claim 4, wherein said rackgear is cocked at a small angle in respect to said pinion gear in orderto permit easy interengagement thereof and to provide a slight pitchinterference during engagement so as to eliminate gear backlash.

6. A motion transmitting device comprising a housing, a rotary inputshaft rotatably mounted in said housing, a rotary and axially movableoutput shaft mounted in said housing for rotatable and axial movement, alever pivoted in said housing and having a drive member engaged withsaid output shaft to move it axially backwardly and forwardly, cam meanson said input shaft including a first cam portion engageable with saidlever to oscillate it backwardly and forwardly in a second cam portion,a slide, means in said housing for guiding said slide from backward andforward movement transverse to the axis of said output shaft, a piniongear carried on said output shaft at a fixed location along its lengthand being engageable with said rack at a predetermined axial position ofsaid output shaft, said slide having follower means engaged with saidsecond cam portion and being movable by rotation of said second camportion backwardly and forwardly, and holder means to hold said outputshaft against rotation at positions of said output shaft when saidpinion gear is out of engagement with said drive gear and to permit easyinterengagement of said gears.

7. A motion transmitting device, according to claim 6, wherein saidsecond cam portion comprises a barrel cam having an outwardly projectingrib cam portion, said slide having a roller engaged with each sidesurface of said ribbed cam portion and comprising said follower means.

8. A motion transmitting device, according to claim 7, wherein saidfirst cam portion comprises a disc cam having a side face with a camgroove therein, said lever having a follower intermediate its lengthengaged in said cam groove.

9. A motion transmitting device, according to claim 6, wherein saidholder means comprises an elongated key affixed in said housing andextending along the axis of said shaft, 21 control plate affixed to saidshaft having at least one set of transversely spaced rollers of a sizeto bear tightly against each side of said key in positions 8 of saidshaft when said pinion gear is out of engagement with said rack. V

,10. A motion transmitting device, according to claim 6, wherein saidinput'shaft is mounted with its axis extending transversely to the axisof said output shaft, said cam means comprising a disc cam forming saidfirst cam portion and a ribbed barrel cam forming said second camportion, said lever follower being engaged with said disc cam, saidslide carrying said rack having a roller engaged on respective sides ofsaid ribbed barrel cam, said rack gear being cocked at a small angle inrespect to said pinion gear for facilitating intermeshing engagementthereof and engagement Without backlash during full engagement.

1]. A motion transmitting device, according to claim 10, including acontrol disc on said output shaft having an annular groove in itscircumference, said driver of said lever engaging into said groove, saidoutput shaft and said slide being mounted in linear ball bearings forrespective axial movements thereof, said plate having a plurality ofcircumferentially spaced pairs of holding rollers engageable with saidkey in accordance with the angular position of said output shaft.

12. A motion transmitting device, according to claim 11, wherein thereare a plurality of keys in said housing extending axially in respect tosaid output shaft.

1. A motion transmitting device, comprising a rotary input shaft havingrotary control cam means thereon, a rotary and axially movable outputshaft having a pinion gear thereon, means supporting said input shaftfor rotary movement and said output shaft for rotary and axial movement,a lever engaged with said cam means and said output shaft and beingmovable by said cam means to shift said output shaft axially, rotarydrive means connected to said cam means and including a drive gear movedby said cam means engageable with said pinion gear to rotate said outputshaft when it is in a predetermined axial position, said pinion gearbeing disengageable from said drive gear to permit axial movementwithout rotation, and holder means to hold said output shaft againstrotation at positions of said output shaft when said pinion gear is outof engagement with said drive gear and to permit easy interengagement ofsaid gears including at least one key elongated in the axial directionof said shaft and fixed in said housing and a control plate affixed tosaid shaft for rotation therewith having a plurality ofcircumferentially spaced pairs of transversely spaced guide rollersadapted to bear along respective sides of said key to hold the saidoutput shaft in a fixed angular position during its linear movement. 1.A motion transmitting device, comprising a rotary input shaft havingrotary control cam means thereon, a rotary and axially movable outputshaft having a pinion gear thereon, means supporting said input shaftfor rotary movement and said output shaft for rotary and axial movement,a lever engaged with said cam means and said output shaft and beingmovable by said cam means to shift said output shaft axially, rotarydrive means connected to said cam means and including a drive gear movedby said cam means engageable with said pinion gear to rotate said outputshaft when it is in a predetermined axial position, said pinion gearbeing disengageable from said drive gear to permit axial movementwithout rotation, and holder means to hold said output shaft againstrotation at positions of said output shaft when said pinion gear is outof engagement with said drive gear and to permit easy interengagement ofsaid gears including at least one key elongated in the axial directionof said shaft and fixed in said housing and a control plate affixed tosaid shaft for rotation therewith having a plurality ofcircumferentially spaced pairs of transversely spaced guide rollersadapted to bear along respective sides of said key to hold the saidoutput shaft in a fixed angular position during its linear movement. 2.A motion transmitting device, according to claim 1, wherein said controlplate has a periphery with a plurality of circumferentially spaced flatchordal mounting surfaces for each of said sets of guide rollers.
 3. Amotion transmitting device, according to claim 1, wherein said drivegear comprises a rack, a slide carrying said rack, means in said housingfor guiding said slide backwardly and forwardly.
 4. A motiontransmitting device, according to claim 3, wherein said cam meansincludes a separate disc cam and ribbed barrel cam with an outwardlyprojecting cam rib, said slide having a roller which is preloadedagainst each side of said cam rib whereby said slide is moved withoutplay backwardly and forwardly.
 5. A motion transmitting device,according to claim 4, wherein said rack gear is cocked at a small anglein respect to said pinion gear in order to permit easy interengagementthereof and to provide a slight pitch interference during engagement soas to eliminate gear backlash.
 6. A motion transmitting devicecomprising a housing, a rotary input shaft rotatably mounted in saidhousing, a rotary and axially movable output shaft mounted in saidhousing for rotatable and axial movement, a lever pivoted in saidhousing and having a drive member engaged with said output shaft to moveit axially backwardly and forwardly, cam means on said input shaftincluding a first cam portion engageable with said lever to oscillate itbackwardly and forwardly in a second cam portion, a slide, means in saidhousing for guiding said slide from backward and forward movementtransverse to the axis of said output shaft, a pinion gear carried onsaid output shaft at a fixed location along its length and beingengageable with said rack at a predetermined axial position of saidoutput shaft, said slide having follower means engaged with said secondcam portion and being movable by rotation of said second cam portionbackwardly and forwardly, and holder means to hold said output shaftagainst rotation at positions of said output shaft when said pinion gearis out of engagement with said drive gear and to permit easyinterengagement of said gears.
 7. A motion transmitting device,according to claim 6, wherein said second cam portion comprises a barrelcam having an outwardly projecting rib cam portion, said slide having aroller engaged with each side surface of said ribbed cam portion andcomprising said follower means.
 8. A motion transmitting device,according to claim 7, wherein said first cam portion comprises a disccam having a side face with a cam groove therein, said lever having afollower intermediate its length engaged in said cam groove.
 9. A motiontransmitting device, according to claim 6, wherein said holder meanscomprises an elongated key affixed in said housing and extending alongthe axis of said shaft, a control plate affixed to said shaft having atleast one set of transversely spaced rollers of a size to bear tightlyagainst each side of said key in positions of said shaft when saidpinion gear is out of engagement with said rack.
 10. A motiontransmitting device, according to claim 6, wherein said input shaft ismounted with its axis extending transversely to the axis of said outputshaft, said cam means comprising a disc cam forming said first camportion and a ribbeD barrel cam forming said second cam portion, saidlever follower being engaged with said disc cam, said slide carryingsaid rack having a roller engaged on respective sides of said ribbedbarrel cam, said rack gear being cocked at a small angle in respect tosaid pinion gear for facilitating intermeshing engagement thereof andengagement without backlash during full engagement.
 11. A motiontransmitting device, according to claim 10, including a control disc onsaid output shaft having an annular groove in its circumference, saiddriver of said lever engaging into said groove, said output shaft andsaid slide being mounted in linear ball bearings for respective axialmovements thereof, said plate having a plurality of circumferentiallyspaced pairs of holding rollers engageable with said key in accordancewith the angular position of said output shaft.